Computer Networks, called Local Area Networks (LANs), are increasingly popular in any environment where more than one computer is being used. Within the IEEE 802.3 protocol (Ethernet), each segment of the LAN can be up to 185 or 500 meters long, depending upon the type of connecting cable that is used. Up to 30 or 100 nodes may be attached to a segment, depending upon the type of cable that is used. Because of this length and number of nodes, a single segment often includes an entire office, and sometimes an entire building with the cable running through cable raceways, between walls and between floors.
The IEEE 802.3 protocol is a carrier sense multiple access/collision detect (CSMA/CD) type of protocol which allows all nodes to timeshare the same cable. When a first node wants to send information to another node, the first node listens for a carrier (meaning that some other node is sending) and if no carrier is sensed, the first node begins to transmit. If two nodes begin transmission at the same time, a collision will occur and both nodes will detect the collision and stop sending. Each node will try again later. Thus all nodes use the same cable without interfering with each other.
If a node is defective it may start sending without first listening for a carrier, which will frequently cause a collision. A defective node may incorrectly detect a carrier, or detect the carrier later than it should, causing a late collision. If a node is misadjusted, it may fail to detect a carrier that is transmitted near the lower limit or upper limit of allowed current.
Each information frame sent on the cable is limited in length, and a defective node may send a frame that is too long. When a frame is too long, any other node on the network may jam the node sending the long frame. If a node is misadjusted, it may send an early jam signal causing a jam of a valid frame.
Many other problems can, and often do, occur on a segment. When a problem occurs, a system administrator needs to know which node is causing the problem. Since all nodes use the same cable, and since this cable may extend for up to 500 meters through walls, cable conduits, and building floors, the administrator has a difficult task in finding the defective node.
There is a need in the art for a system to locate nodes on a network segment. There is a further need for such a system that will detect nodes that cause late collisions. A still further need is for such a system that detects nodes that cause early jamming. Yet another need is for a system to detect nodes that fail to detect carrier levels near the allowable limits. The present invention meets these needs.